The invention relates to a hemodiafiltration apparatus comprising a dialyzer which is divided by a membrane into two chambers, the first chamber being connected into a dialysis solution path and the second chamber into a blood path, the dialysis solution path comprising a supply line which extends from a means for preparing dialysis solution up to the dialyzer and into which a first balance chamber is connected, and a discharge line which extends from the dialyzer to the discharge and into which a second balance chamber is connected, a pump for conveying dialysis solution in the closed dialysis solution system, an ultrafiltration means provided between the balance chambers in the dialysis solution path, a connecting line which branches from the supply line between the first balance chamber and the dialyzer and which is connected to the blood path and into which at least one sterile filter and a pump are connected, and a drip chamber and a blood pump in the blood path.
In hemodiafiltration, in a manner similar to hemodialysis, blood is conducted past the membrane of a hemofilter, part of the serum being withdrawn via the membrane. This part is replaced by a sterile substitution liquid which is added to the extracorporeal blood path either upstream of the dialyzer (predilution) or downstream of the dialyzer (postdilution). In addition, in the diafiltration the usual hemodialysis is carried out, i.e. at the membrane of the hemodialyzer dialysis solution is led past so that across the membrane an exchange of substances usually eliminated with urine can take place.
Generally, at present substitute solutions are made available by manufacturers who produce infusion solutions and the like. Accordingly, relatively large-volume containers are made by the manufacturer which contain sterile and pyrogen-free substitute and thereafter brought to the patient, this involving high costs with the result that due to said high substitute costs hemofiltration has not been able to establish itself particularly well.
For this reason attempts have already been made to produce the substituate solution on-line, i.e. at the bedside, in that the usual dialysis solution is transformed to the sterile and pyrogen-free state and the substituate thereby obtained thereafter administered to the patient.
From the Trans. Am. Soc. Artif. Intern. Organ (ASAIO), 1978, p. 465-467, the on-line production of a sterile and pyrogen-free substitute is known which is made by employing the usual proportioning unit for making the conventional dialysis solution. A concentrate is mixed in a ratio of 1:34 with water, the dialysis solution thereby produced degassed and heated and thereafter supplied to two ultrafilters which are connected in series. At the end of the second filter sterile and pyrogen-free substituate is obtained which is then supplied to the blood path.
In this preparation procedure the delivery pump is thus upstream of the two ultrafilters which has however not been found expedient. For the delivery pump is on the pressure side of the first filter and thus conveys the particles and germs contained upstream of the ultrafilters in the dialysis solution under pressure into the first ultrafilter. This results in the so-called closed-end effect, i.e. the particles conveyed under pressure rapidly clog the ultrafilter and consequently this arrangement has not proved itself in practice. DE-OS No. 3,407,147 discloses an apparatus for preparing medical infusion solutions in which a concentrate liquid and pure water are mixed together in a mixing container in a predetermined ratio. After the mixing the mixture obtained is applied with the aid of a pump to only one ultrafilter so that in this case as well the same disadvantages as in the arrangement mentioned above occur, i.e. the socalled closed-end effect again results.
From ASAIO 1979, p. 404-408, a further on-line substituate producing unit is known which corresponds substantially to the unit explained above, i.e. once again two ultrafilters are disposed in the dialysis solution path. In addition, however, downstream of these two filters a delivery pump is connected into the substituate delivery path but this is also disadvantageous because the pressure drop across the two ultrafilters is too high and as a result these pumps operate in the vacuum region. A consequence of this is that the usually flexible substituate stituate solution is no longer possible. In addition, this substituate is again degassed and this is extremely undesirable for medical reasons.
EP-OS No. 42,939 discloses a hemofiltration system which proceeds from the apparatuses mentioned above with the provision that only one ultrafilter is used for sterilizing the dialysis solution. This filter must be specially monitored to detect immediately any leak occurring. This relatively complicated apparatus is eliminated in the aforementioned systems by the provision of two filters, which for economic reasons is substantially more advantageous and moreover technically simpler.